A house is a noble dynasty. There are great houses and vassal houses. Great houses are noble families of great power. They rule over their own realm and are supported by a number of vassal houses. A vassal house is simply a noble family of lower social rank. Vassals lack the wealth, might, and/or reputation required to hold dominion over large realms or command massive armies.
The King & the Barons
In Kavania, heads of vassal houses are called barons. Barons lord over baronies, and traditionally hold fealty to the king and his royal house. If the king calls upon them, they are ordered to come, providing support in whatever way the crown demands. Their armies are usually at least a few thousand strong. Barons are expected to hold lofty castles and rule over many underlings, and in a time where there is no proper king, they are for all practical purposes now lesser kings and queens in their own right.
Counts
There are also lesser houses, which are even lower ranking noble families, which are headed by counts. These counts serve a vassal house similarly in the way their vassal house serves the royal house. Counts tend to their counties (multiple counties make up a barony) and usually command smaller armies of a few thousand but more often less.
Viscounts
Viscounts are the lowest ranking nobility in the realm, being equal to landed knights. They are often families of important people in the land who were given the title for noble or nefarious reasons or another. "Viscount" is a rather new title, only having been used since the rule of King Lain Fairborn, and as such these families are never more than a few centuries old. Viscounts command smaller lands and personnel still.
Landed Knights
A landed Knight is a knight that takes residence in a keep with accompanying land. They have their own peasants and men-at-arms and may take sworn swords. They are the lowest ranking members of nobility, along with the viscounts. Too low of status to marry into a barony, or enact punishment on their smallfolk in their own lands. For this, a landed knight must appeal to a higher ranking noble, usually a count or baron. is a knight that takes residence in a keep with accompanying land. They have their own peasants and men-at-arms and may take sworn swords.
Other Noble Titles
In realms outside of Kavania, other peoples may call their masters different titles, or have completely different governing customs. A clan for example, would be a group of families